Ethylene and ethylene derivatives are widely used in the manufacturing of many of today's plastics. Ethylene is typically obtained by the cracking of hydrocarbons, such as natural gas condensates and petroleum distillates, which include ethane and higher hydrocarbons. Ethylene is then obtained by separation from the cracked product mixture.
Cracking processes are well known in the chemical processing industry. These processes require high temperatures. In the production of ethylene, gaseous, or light liquid hydrocarbons are heated to temperatures ranging from about 750° C. to about 950° C. Typically, in cracking processes to produce ethylene, both ethane and ethylene are produced. The resulting product mixture is usually subjected to elaborate separation steps in order to remove ethylene. This method of producing ethylene is usually very energy intensive.
Multiple separation steps are typically needed in order to recover ethylene from the cracked product stream. These multiple separation steps can be costly in capital expenditures and in energy costs.
Another process that is theoretically possible to produce ethylene is the coupling of methane. Methane is the most abundant component in natural gas and is generally less expensive a feed compared with the typical ethylene cracker feedstock, such as ethane and other higher hydrocarbons. Ethane and ethylene can be produced from methane by the oxidative coupling of methane. In such a process, oxygen and methane are fed into a reactor at elevated temperatures. This process avoids some of the costs associated with cracking processes. However, the reactions involved are highly exothermic and thus such a process is performed under very high temperatures. Such high temperatures can prove difficult in controlling the reaction conditions.
Oxidative coupling also encompasses reactions other than methane coupling, for example, reactions between methane and toluene. These oxidative coupling reactions are also highly exothermic. A need exists to regulate the heat of reaction in order to control the oxidative coupling reaction.
In many processes, including ethylene production processes, steam is utilized to provide necessary heat. Typically steam is produced by combustion of an outside fuel source, such as coal or natural gas, in separate boilers. In certain cracking processes, steam is used to provide the necessary heat for the cracking reaction. Other typical uses for steam include supplying heat to a heat exchanger, supplying heat to a reboiler, and supplying energy to a turbine to drive a compressor. Since typical steam production uses fuel as a heat source, such steam production can be costly, especially when fuel prices are high. A need exists to supply steam in an efficient manner.
In view of the above, it would be desirable to have a process to produce ethylene, which does not rely completely on cracking and expensive separation technologies. It would also be desirable to have an ethylene process that is able to make use of a less expensive feedstock than ethane and heavier hydrocarbons. It would also be desirable to effectively control the exothermic conditions typically associated with methane coupling reactions. In addition, it would be desirable to provide for the generation of steam needed for a process in an efficient manner.